Known in the prior art are aircraft wheel and brake assemblies including a non-rotatable wheel support, a wheel mounted to the wheel support for rotation, and a brake disk stack having front and rear axial ends and alternating rotor and stator disks mounted with respect to the wheel support and wheel for relative axial movement. Each rotor disk is coupled to the wheel for rotation therewith and each stator disk is coupled to the wheel support against rotation. A back plate is located at the rear end of the disk pack and a brake head is located at the front end. The brake head houses a plurality of actuator rams that extend to compress the brake disk stack against the back plate. Torque is taken out by the stator disks through a static torque tube or the like.
Prior art brake systems typically implement electrically operated actuator rams or hydraulically operated actuator rams, although some brakes may use pneumatically operated actuator rams. In brake systems that employ fluid powered (hydraulic or pneumatic power) actuator rams, the actuator ram is coupled to a power source via a brake servo valve and a safety interlock valve. The safety interlock valve effectively functions as a shutoff valve, wherein in a first position (e.g., an armed position) fluid pressure is permitted to pass through the valve, while in a second position (e.g., a disarmed position) fluid pressure is prevented from passing through the valve. During normal braking, the safety shutoff valve is in the armed position, thereby permitting the flow of fluid pressure. The brake servo valve, based on braking commands from the pilot and/or computer controlled braking, controls the amount of fluid pressure provided to the actuator ram and, thus, the braking force applied to the wheel.
To prevent unintentional braking (e.g., due to a faulty servo valve) during takeoff, the shutoff valve is set in the disarmed position, thereby removing fluid pressure from the servo valve. Since the servo valve does not receive fluid pressure, it cannot provide fluid pressure to the actuator ram and, thus, braking cannot be effected.